These studies have continued to focus on the mechanism by which plasma lipoproteins deliver lipids to cultured cells. Using chylomicrons and Lp(a) we have shown that the presence of apolipoproteins B and E in these lipoproteins does not assure binding to the high affinity receptor. Partial delipidation of these lipoproteins renders them capable of binding and suggests that the interaction of these apolipoproteins with lipid is also important in the binding process.